Mistertower, you stole most of my thunder. I was going to offer that during my youth, when I was doing a lot of cab-riding on the Santa Cruz Branch, the regular hogger, Al Davies gave me the poop on red Gyralites, as this was one of my favorite aspects of SP locomotives. As you also said, both Gyralites were manually switchable, but the red one could also be activated by low air pressure. Of course an emergency application would qualify as low pressure, but he seemed to indicate that it came on when trainline air was below 60 or 70 pounds. Al would turn the red Gyralite on for me on some nights when he passed by my house in Capitola, as he knew I loved to see it. I also remember following the Sunset westbound up the grade from above Palm Springs to Beaumont in 1962 and I can remember seeing the observation (last car at least) car's red gyralite for miles behind the train. I also remember seeing a GP-20 (think it may have been Cotton Belt) with the red Gyralite on as it crawled into the receiving track area at Kaiser Steel in Fontana in '65. I think it was easy for the crew to forget that it was on in the daylight. The good old days.